The present invention relates to printing devices. More particularly, the present invention relates to an apparatus and method of measuring dry time of printing composition.
Printing devices, such as inkjet printers and laser printers, use printing composition (e.g., ink or toner) to print text, graphics, images, etc. onto print media. Inkjet printers may use print cartridges, also known as "pens", which shoot drops of printing composition, referred to generally herein as "ink", onto a print medium such as paper or transparencies. Each pen has a printhead that includes a plurality of nozzles. Each nozzle has an orifice through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page by, for example, a carriage, while shooting drops of ink in a desired pattern as the printhead moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as thermal printhead technology. For thermal printheads, the ink may be a liquid, where dissolved colorants or pigments are dispersed in a solvent.
In a current thermal system, a barrier layer containing ink channels and vaporization chambers is located between an orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heating elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, the ink in the vaporization chamber turns into a gaseous state and forces or ejects an ink drop from a orifice associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the print medium, the ink is expelled in a pattern onto the print medium to form a desired image (e.g., picture, chart or text).
In order for the image to be fixed to the print media so that it will not smear, the ink must be dried. The ink is dried by a combination of the solvent evaporating and the solvent absorbing into the print medium, both of which take time. Various factors control the amount of time required for a particular ink to dry. These factors include the type of print media, the quantity of solvent in an ink, the amount of ink on the print media, and ambient temperature and humidity. To reduce the amount of this time, the surface of some types of print media may be specially coated to help speed drying. Other means may also be used such as special chemicals generally know as "fixers" that are applied to print media before or after printing. Various types of heating devices may also be used to heat print media before and/or after printing.
Irrespective of how drying is accomplished, it is useful to know printing composition dry time for a particular combination of printing composition, print medium, printing device, and ambient conditions. Such information can be used by a printing device to help prevent image smear, print media cockle (print media buckle toward a printhead), and print media curl (curling along at least one edge of a print media), as well as help maximize printing device throughput.
Accordingly, the present invention is directed to measuring printing composition dry time to help prevent the above-described problems and optimize printing. The present invention accomplishes this without degrading output print quality of a printing device.
An embodiment of a detection system in accordance with the present invention for measuring a dry time of a printing composition used by a printing device includes a source, a sensor, and a controller. The source is configured to transmit a first light signal toward a quantity of printing composition deposited on a print medium. The printing composition reflects a second light signal in response to illumination by the first light signal. The second light signal has a magnitude that decreases to a substantially constant value as the printing composition dries over a period of time. The sensor is configured to detect the second light signal and convert the second light signal into an electrical signal having a value proportional to the magnitude of the second light signal. The controller is coupled to the sensor and is configured to receive the electrical signal from the sensor over the period of time the printing composition dries. The controller is also configured to determine a dry time for the printing composition based upon the electrical signal.
The above-described embodiment of a detection system of the present invention may be modified and include the following characteristics described below. The controller may be further configured to adjust an operating parameter of the printing device based upon the determined dry time. The source may include a light emitting diode and the sensor may include a photodiode. The print media detection system may be used in a printing device.
An alternative embodiment of a detection system in accordance with the present invention for measuring a dry time of a printing composition used in a printing device includes structure for illuminating a printing composition subsequent to deposition on a print medium. The detection system also includes structure for measuring over a selected period of time a quantity of light reflected by the printing composition subsequent to illumination. The detection system further includes structure for determining a dry time for the printing composition based upon the measured quantity of light reflected by the printing composition over the selected period of time.
The above-described alternative embodiment of a detection system of the present invention may be modified and include the following characteristics described below. The detection system may further include structure for adjusting at least one operating parameter of a printing device based upon the dry time. The detection system may further include structure for depositing the printing composition on the print medium. In such cases, the depositing structure may include an inkjet printhead. The detection system may be used in a printing device.
An embodiment of a method in accordance with the present invention of measuring a dry time of a printing composition used by a printing device includes depositing a quantity of printing composition onto a print medium and illuminating the printing composition subsequent to printing. The method additionally includes measuring over a selected period of time a quantity of light reflected by the printing composition in response to illuminating. The method further includes determining a dry time for the printing composition based upon the measured quantity of light reflected by the printing composition over the selected period of time.
The above-described embodiment of a method of the present invention may be modified and include the following characteristics described below. Depositing may include placing a plurality of drops of printing composition onto the print medium. Depositing may include selecting a number of drops of printing composition to place onto the print medium. Each of the drops may have a volume substantially equal to a selected volume.
The method may additionally include adjusting at least one operating parameter of a printing device based upon the determined dry time. Illuminating and measuring may include optically scanning the printing composition. The method may be used in a printing device.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.